1. Field of the Invention
The present invention relates to power conversion devices capable of converting an electric power of a power source device such as a battery to a drive power so as to drive an electric motor, etc.
2. Description of the Related Art
For example, a power conversion device is used for converting an electric power of a power source device to a drive power so as to drive an electric motor, etc. There are various types of the power conversion devices, for example, an inverter, and a converter.
A switching loss is generated in a power conversion device due to a switching operation of turning ON/OFF switching elements in the power conversion device. In order to reduce such a switching loss, there has been proposed a technique to perform zero-voltage switching (hereinafter, referred to as the “ZVS”) to reduce the switching loss. The technique uses a resonance phenomenon of a reactor and a capacitor.
Patent document 1, Japanese patent NO. 3207431, shows a zero-voltage transition voltage source inverter capable of converting a direct current power of a direct current power source to a three phase alternating current power. The zero-voltage transition voltage source inverter has a switching bridge and an auxiliary circuit. The switching bridge is arranged between input terminals of the direct current power source and output terminals of the three phase alternating current power. The auxiliary circuit is arranged between input terminals of the direct current power source and the switching bridge.
The auxiliary circuit is composed of a rail switch, a series connection part and an auxiliary diode. The rail switch is connected to a direct current rail of the input terminals of the direct current power source. The series connection part is composed of a resonance inductor and an auxiliary switch. A first terminal of the auxiliary diode is connected to a connection node between the auxiliary switch and the resonance inductor. A second terminal of the auxiliary diode is grounded.
In the control method disclosed in Patent document 1 previously described, the bridge switch of the bridge circuit is turned on when the rail switch of the direct current rail is in an OFF-state. Next, the rail switch is turned on at a timing t1 by the auxiliary circuit.
The auxiliary switch of the auxiliary circuit is turned on before time t1, energy capable of flowing a current is accumulated in the resonance inductor, and the auxiliary switch is turned off after the timing t1. The resonance switch resonates with the capacitor arranged between the bridge switch and the rail switch, and provides a zero current transition corresponding to the turn-on switching of the rail switch. After this, the bridge switch is turned off, and the rail switch is turned off.
However, the control method disclosed by the patent document 1 previously described provides an excessive current when the auxiliary switch operates in addition to a necessary current for the ZVS, and this increases a power loss of the auxiliary switch. There are various methods regarding a power consumption technique using the ZVS, for example, a feedback control method of adjusting a switching timing on the basis of current and voltage information so as to reduce the current as low as possible, or a method of detecting a load current and a current flowing in the auxiliary circuit by using a current sensor, and calculating the current on the basis of a logical expression the by using a control circuit, etc. However, when the control method cannot follow a rapid change of the load current and the ZVS does not correctly operate, the magnitude of the switching loss increases.